全文获取类型
收费全文 | 133998篇 |
免费 | 6163篇 |
国内免费 | 3097篇 |
专业分类
电工技术 | 4222篇 |
技术理论 | 6篇 |
综合类 | 6198篇 |
化学工业 | 19667篇 |
金属工艺 | 7457篇 |
机械仪表 | 6280篇 |
建筑科学 | 6480篇 |
矿业工程 | 2094篇 |
能源动力 | 2799篇 |
轻工业 | 7391篇 |
水利工程 | 2317篇 |
石油天然气 | 2753篇 |
武器工业 | 542篇 |
无线电 | 15183篇 |
一般工业技术 | 21940篇 |
冶金工业 | 4711篇 |
原子能技术 | 864篇 |
自动化技术 | 32354篇 |
出版年
2024年 | 189篇 |
2023年 | 960篇 |
2022年 | 1686篇 |
2021年 | 2422篇 |
2020年 | 1794篇 |
2019年 | 1501篇 |
2018年 | 15885篇 |
2017年 | 15006篇 |
2016年 | 11402篇 |
2015年 | 2827篇 |
2014年 | 2949篇 |
2013年 | 3405篇 |
2012年 | 6726篇 |
2011年 | 12993篇 |
2010年 | 11685篇 |
2009年 | 8811篇 |
2008年 | 9909篇 |
2007年 | 10511篇 |
2006年 | 2911篇 |
2005年 | 3417篇 |
2004年 | 2698篇 |
2003年 | 2487篇 |
2002年 | 1958篇 |
2001年 | 1348篇 |
2000年 | 1283篇 |
1999年 | 1182篇 |
1998年 | 886篇 |
1997年 | 740篇 |
1996年 | 714篇 |
1995年 | 516篇 |
1994年 | 468篇 |
1993年 | 320篇 |
1992年 | 287篇 |
1991年 | 215篇 |
1990年 | 145篇 |
1989年 | 129篇 |
1988年 | 89篇 |
1987年 | 55篇 |
1986年 | 41篇 |
1968年 | 43篇 |
1967年 | 34篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1960年 | 30篇 |
1959年 | 38篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
31.
Mobile software applications have to cope with a particular environment that involves small size, limited resources, high autonomy requirements, competitive business models and many other challenges. To provide development guidelines that respond to these needs, several practices have been introduced; however, it is not clear how these guidelines may contribute to solve the issues present in the mobile domain. Furthermore, the rapid evolution of the mobile ecosystem challenges many of the premises upon which the proposed practices were designed. In this paper, we present a survey of the literature on software assurance practices for mobile applications, with the objective of describing them and assessing their contribution and success. We identified, organized and reviewed a body of research that spans in three levels: software development processes, software product assurance practices, and software implementation practices. By carrying out this literature survey, we reviewed the different approaches that researchers on Software Engineering have provided to address the needs that raise in the mobile software development arena. Moreover, we review the evolution of these practices, identifying how the constant changes and modernization of the mobile execution environment has impacted the methods proposed in the literature. Finally, we introduced discussion on the application of these practices in a real productive setting, opening an area for further research that may determine if practitioners have followed the proposed assurance paradigms. 相似文献
32.
33.
This paper presents an integrated passive damping approach in hybrid metal-CFRP parts for structural applications. In this concept a viscoelastic material is embedded in the joint zone of the hybrid component. To examine the connection strength single-lap-joint specimens were produced and tested and the influence of the used material combinations, different surface structures, and different process parameters i.e. the moment of cross-linking were evaluated. Afterwards, the metal-CFRP hybrids were tested in quasi-static tests to assess their connection strength and failure behaviour. Dynamic cyclic tensile tests with step-wise increased loading conditions were performed to determine the specimens damping behaviour and to estimate their fatigue performance. Finally, these results are compared to a state of the art metal-CFRP hybrid with rivets connecting both materials. 相似文献
34.
采用正硅酸乙酯(TEOS)和3-氨丙基三乙氧基硅烷(APTES)通过共缩聚法合成介孔二氧化硅(MCM-41)。首先对其氨基修饰,再通过有机合成接枝—R基团(—R:—CHO、—OH、—CH3、—COOH),制备得到Me-Ph-NH-MCM-41、OHC-Ph-NH-MCM-41、HO-Ph-NH-MCM-41、HOOC-Ph-NH-MCM-41四种不同的药物载体。利用FT-IR、Zeta电位、XRD和SEM对其结构和形貌表征,结果表明NH2-MCM-41改性成功。以罗丹明B(RhB)为模型进行载药性能测试,并考察了此释药系统在模拟不同pH的体液下的敏感释药行为,同时探究了不同—R基团对释药的影响。结果显示,四种载体在中性条件下几乎不发生药物释放,通过改变环境体系pH可以有效控制药物释放,其释药行为可以用Korsmeyer-Peppas动力学模型来描述。实验表明,释药量:RhB@HOOC-Ph-NH-MCM-41>RhB@OHC-Ph-NH-MCM-41>RhB@HO-Ph-NH-MCM-41>RhB@Me-Ph-NH-MCM-41,不同—R基团的药物载体的pH响应性不同,其中RhB@HOOC-Ph-NH-MCM-41释药量在pH=1.2时可达57.87%,在用于药物智能控释材料方面具有一定的应用潜力。 相似文献
35.
In this paper, we consider the classical finite mixture model, which is an effective tool for modeling lifetime distributions for random samples from heterogeneous populations. We discuss new results on stochastic comparison for two finite mixtures when each of them is drawn from one of the following semiparametric families, i.e., proportional hazards, accelerated lifetime and proportional reversed hazards. 相似文献
36.
37.
38.
Variations of Incomplete Open Cubes is the major project by the twentieth-century conceptual artist Sol LeWitt. In this paper we interpret the enumerative component of the project as embeddings of graphs. This formulation permits use of an algorithm to check the completeness of the list of the structures produced by the artist. Our conclusion is that the artist found the correct number of structures (that is, 122), but that his list contains a mistake in the presentation of a pair of incomplete cubes, a discovery that appears not to have been noted before. 相似文献
39.
Debin Wang Jingsong Liu Mengshi Zeng Chunmei Zhang Huiqin Li Hongtao Yu Ying Yuan Shuren Zhang 《Journal of the American Ceramic Society》2019,102(7):4029-4037
(1-x)Sr0.7Pb0.15Bi0.1TiO3-xBi4Ti3O12 ((1-x)SPBT-xBIT, x = 0-0.125) bulk ceramics were developed and calcined via the solid-state method, aimed at the application of pulsed power capacitors. The phase structures, temperature stability, hysteresis loop, and discharge properties were systematically investigated. Considering both the temperature stability and dielectric properties, 0.925SPBT-0.075BIT bulk ceramics with a capacitance variation satisfying the X7R specification were developed for pulsed power capacitors. The energy storage density was 0.252 J/cm3, and the ceramics showed high temperature stability at 80 kV/cm. The discharge current waveforms of the 0.925SPBT-0.075BIT ceramics were recorded. A high discharge power density of approximately 1.01 × 108 W/kg with an 8 Ω load resistor and short discharge period of 84 ns were achieved at 50 kV/cm. The good temperature stability properties and high power density show that the 0.925SPBT-0.075BIT ceramics are well suited for pulsed power capacitors with a wide temperature range. 相似文献
40.
Multifunctional 3D Patternable Drug‐Embedded Nanocarrier‐Based Interfaces to Enhance Signal Recording and Reduce Neuron Degeneration in Neural Implantation 下载免费PDF全文